1. Field of the Invention
This invention relates to an improvement in a method of controlling the speed of a motor. This invention particularly relates to an improvement in a method of controlling the speed of a low-speed motor mounted on a supporting base the position of which is changed by rotation, swinging or the like when the motor is operating.
2. Description of the Prior Art
In portable audio apparatuses such as cassette decks and radiation image recording and read-out systems using a stimulable phosphor as described, for example, in Japanese Patent Application No. 57(1982)-193767, which are placed and used in a vehicle, the motors used therefor are mounted on supporting bases the positions of which are changed during operation of the motor installations. In the motors of this type, the stator is subject to the same movement as that of the supporting base, and the rotor is required to undergo a desired movement with respect to the stator.
In the aforesaid motors, when a change in the position of the supporting base causes a change in angular velocity in a plane normal to the shaft of the motor, namely when angular acceleration arises with respect to the shaft of the motor, the change in the position of the supporting base causes the rotation speed of the motor to change. This occurs because the rotor has inertia and tends to maintain the previous movement including that of the supporting base carrying the motor thereon.
In order to control the speed of the motor the rotor of which is subject to a movement relative to the stator, it is necessary to regulate speed control so as to compensate for the movement of the rotor relative to the stator. The compensation for the movement of the rotor relative to the stator is of course not necessary when the movement is at a constant angular velocity, but is necessary only when such movement involves angular acceleration of the motor shaft. Actually, the aforesaid compensation is found to be significant only when the degree of angular acceleration generated with respect to the shaft of the motor by the aforesaid relative movement is significantly large with respect to the rotation speed of the rotor of the motor.
Although there have been such motors wherein the stator undergoes movement which is likely to disturb the rotation speed of the rotor, in general, the degree of angular acceleration of the stator relative to the rotor was very small with respect to the rotation speed of the rotor so that there were few cases where compensation for the movement of the supporting base relative to the rotor was required.
However, in the aforesaid radiation image recording and read-out systems using a stimulable phosphor, or the like, the rotation speed of the rotor of the motor used in the systems is very low and, in general, ranges from about 0.4 rpm to 2 rpm. On the other hand, the degree of angular acceleration produce by the movement of the supporting base on the shaft of the motor is nearly 200 mrad/sec.sup.2. Therefore, the effect of the movement of the supporting base on the rotation speed of the rotor is not negligible. In the speed control of the motor used in the aforesaid new applications, it is desirable to eliminate the adverse effect of a change in the position of the stator supporting base on the rotation speed of the rotor.
The primary object of the present invention is to provide a method of controlling the speed of a motor supported on a supporting base the position of which is changed during operation of the motor, the method eliminating the adverse effect of the movement of the supporting base on the rotation speed of the rotor.
Another object of the present invention is to provide a method of controlling the speed of a motor supported on a supporting base the position of which is changed during operation of the motor, the method being very suitable for the speed control of a low-speed motor supported on such a supporting base.